# voltage and current amplifier

Discussion in 'Homework Help' started by bhuvanesh, Mar 10, 2015.

1. ### bhuvanesh Thread Starter Member

Aug 10, 2013
268
2
voltage amplifier does voltage amplification
current amplifier does current amplification

Is there something like power amplifier or power amplifier is just same as current amplifier?

2. ### Dodgydave AAC Fanatic!

Jun 22, 2012
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A power amplifier is used to boost signal levels to drive a loudspeaker, it does both , amplifies the voltage of the signal, and drives a low impedance load at high current.

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3. ### bhuvanesh Thread Starter Member

Aug 10, 2013
268
2
ASSUME:if suppose a speaker having low impedance ,then power amplifier want to amplifies the current of signal to drive the speaker
ASSUME:if suppose a speaker having high impedance ,then power amplifier want to amplifies the voltage of signal to drive the speaker
am i right?

4. ### MrChips Moderator

Oct 2, 2009
14,298
4,199
According to Ohm's Law, I = V/R.

So for a fixed resistance R, current I is proportional to the applied voltage V.

For higher power, both V and I have to increase.

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5. ### bhuvanesh Thread Starter Member

Aug 10, 2013
268
2
the below line is from my book
"power amplifier provide modest amount of voltage gain but substantial current gain"
okay ,by ohms law i proportional for v ,i agree,but the above statement does not seems like i proportional to v,does it?
This is the reason why i asked does the power amplifier amplify current alone.

6. ### Dodgydave AAC Fanatic!

Jun 22, 2012
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a power amplifier can increase either the Voltage or the Current, or both.

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7. ### bhuvanesh Thread Starter Member

Aug 10, 2013
268
2
okay another question which is slight away form this topic,sorry if the question is very basic
• output of microphone (transducer) is voltage signal(voltage varying with time)
if the power amplifier want to amplify the current of this signal ,how could it be, because output of transducer is voltage signal not current signal.
help me understand this.Thank you

8. ### MrChips Moderator

Oct 2, 2009
14,298
4,199

So what happens when the speaker is medium impedance? Is it current amplifier or voltage amplifier.

It is all about resistance and impedance.

A high resistance will draw very low current. Hence you need high voltage to deliver power.
A low resistance will draw high current even when the voltage is low. Hence you need a power supply that can deliver current.

Power amplification comes from the power supply, not the signal.
If the load is high impedance, you need a high voltage power supply, i.e. a power supply that can deliver high voltage.
If the load is low impedance, you need a high current power supply, i.e. a power supply that can deliver high current.

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9. ### bhuvanesh Thread Starter Member

Aug 10, 2013
268
2
This is what i said too,may be the phrasing was wrong,Thank you

10. ### MrChips Moderator

Oct 2, 2009
14,298
4,199
Suppose you have a sensor with 10kΩ source impedance with an output signal of 1V.

And you need to drive a 10Ω load with a 2V signal.

Do you need a current amplifier or voltage amplifier?

Answer: You need a voltage gain of x2. You need an output amplifier that can supply 200mA, minimum.

(The input impedance of the amplifier should be much greater than 10kΩ, at least 100kΩ).

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11. ### anhnha Well-Known Member

Apr 19, 2012
783
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Did you mean output impedance?

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12. ### bhuvanesh Thread Starter Member

Aug 10, 2013
268
2
here we need voltage amplification,because the source impedance of sensor is high,in order to drove that we need high voltage,right?
Here we need current amplification since the load impedance is low,so need to amplify the current,right?

13. ### bhuvanesh Thread Starter Member

Aug 10, 2013
268
2
No,its input impedance of amplifier between sensor and load ,it should be high else we lose information from sensor.